The present invention relates to an improved plasma processing method and products thereof. More particularly, but not exclusively, it relates to a method of adhering a protective film of carbonaceous material to comparatively soft substrates in order to provide a transparent electrically insulating coating thereon.
Hard, thin films of diamondlike carbon have been deposited on substrates in a number of ways. By "diamondlike carbon" is meant carbon with exceptional hardness, e.g. which can neither be cut with a razor blade nor scratched by rubbing with steel wool. The chemical bonding of such diamondlike carbon appears to be dominated by sp.sup.3 tetrahedral diamondlike bonding as opposed to the sp.sup.2 trigonal bonding of graphite. Diamondlike carbon films may or may not give evidence of crystallinity by x-rays.
Japanese Patent Application No. Sho 56-146936 describes a process in which carbon deposition is carried out with the deposited carbon material being subject to the attack by accelerated ions at the same time so that soft portions of the deposited material are selectively removed to leave comparatively hard material. This technique is excellent for increasing the hardness of the carbon film thus deposited. The carbon being deposited, however, tends to penetrate into the underlying substrate. FIGS. 1(A) and 1(B) shows an example. A carbon film 2 was deposited on a Si substrate 3 by chemical vapor reaction. The substrate was then subjected to Auger analysis in order to investigate the distribution of carbon atoms and Si atoms along the depth direction. As a result, a mixture film was formed at the interface between the substrate 3 and the carbon film 2 as shown in FIG. 1(B). The silicon carbon mixture is relatively soft and tends to increase liklihood of causing the carbon film to come off from the underlyin substrate particularly when the carbon film has been relatively thick.
Furthermore, when fluorine is desired to be introduced into carbon films in order to control the transparency and the resistivity or to improve the hydrophilic property of the carbon films, the underlying surface to be coated is exposed during the deposition to a caustic fluorine gas and may be damaged.